Yes, oak is a Scrabble word!
...and is worth 7 points in Scrabble, and 7 points in Words with Friends
oak
Noun
1. The hard durable wood of any oak; used especially for furniture and flooring
2. A deciduous tree of the genus Quercus; has acorns and lobed leaves
What Scrabble words can I make with the letters in oak?
3 Letter Words
2 Letter Words